There have been conventionally known exhaust emission control devices provided in exhaust gas passage of an internal combustion engine for collecting particulates in exhaust gas exhausted from the internal combustion engine such as a diesel engine, as well as reducing amount of NOx contained in the exhaust.
As exhaust emission control devices for collecting the particulates, there have been developed devices provided with a DPF (Diesel Particulate Filter); while as exhaust emission control devices for reducing amount of the NOx (nitrogen oxide), there have been developed devices provided with a DeNOx catalyst such as a NOx reducing catalyst, a NOx adsorption catalyst etc.
Particularly, in order to cope with tight control on exhaust emission in recent years, there have been developed exhaust emission control devices formed by combining in series a DPF and a DeNOx catalyst (see Document 1, for example). With such an exhaust emission control device, particulates can be collected by the DPF in a front-stage of an upstream side, and NOx can be reduced by the DeNOx catalyst in a rear-stage on a downstream side, so that purification performance of exhaust gas can be further improved.
To allow the NOx reducing catalyst to react with the exhaust, a reducing agent is supplied from the upstream side of the exhaust gas passage. Though the reducing agent can be atomized into fog by means of high pressure injection so as to be supplied, in most case the reducing agent is atomized by being mixed with air. Further, as for atomization by being mixed with air, in the case of an engine equipped with an exhaust turbocharger, it is proposed that a part of the supercharged air from a supercharger side be supplied to a reducing agent sprayer, and the reducing agent be atomized by the air (see Document 2, for example).                [Document 1] Japanese Patent Laid-Open Publication No. 2000-199423 (FIG. 1 etc.)        [Document 2] Japanese Patent Laid-Open Publication No. Hei07-102949 (FIG. 1 ect.)        